The present invention relates generally to the storage of data on magnetic recording tape, and in particular, to the storage of data on magnetic tape in cartridge form.
In the course of developing various systems for the storage of data on magnetic recording tape, particularly off-line storage of data in the form of back-up storage, a variety of different formats have been developed. Many of these formats call for the tape to be contained in an appropriate cartridge, both to facilitate handling of the tape while in use, and to protect the tape while in storage.
Recently, IBM Corporation has announced a tape cartridge which is primarily intended for use in its Model 3480 data storage system, for the storage of relatively large quantities of data (on the order of 200 megabytes). Details regarding the construction of this type of tape cartridge (hereinafter referred to as a 3480 tape cartridge) may be had with reference to U.S. Pat. No. 4,452,406. By way of general description, the 3480 tape cartridge is comprised of a single reel containing a quantity of magnetic tape and contained in a rectangular enclosure having dimensions on the order of 4 inches in width, 5 inches in length, and 1 inch in height. The cartridge enclosure includes an aperture in one of its major faces, to receive means for rotating the reel of tape contained within the cartridge, and an aperture in one of its corners, for gaining access to the free end of the web of tape. A so-called "leader block" is connected to the free end of the tape, and is frictionally received within the open corner of the cartridge so that it is capable of being withdrawn from and replaced within the cartridge by appropriate means.
In connection with the 3480 tape cartridge, IBM Corporation has also developed equipment for receiving the tape cartridge and for properly placing the web of tape which it contains in operative association with a magnetic read/write head. Further details regarding such equipment may be had with reference to U.S. Pat. Nos. 4,432,508; 4,399,959; 4,399,936; and 4,335,858, which illustrate various different devices which have been developed by the IBM Corporation to accommodate its 3480 tape cartridge.
Unlike many of the other types of tape cartridges which have been developed for use in the off-line storage of data, the IBM 3480 tape cartridge houses only a single reel of magnetic recording tape. The leader block which is connected to the free end of the web of tape is used to introduce the web of tape to the transport apparatus (and the read/write head). To this end, the transport apparatus must be provided with appropriate means for withdrawing the leader block from its nesting within the 3480 tape cartridge, and for threading the leader block (and the web of tape) through the apparatus and past the read/write head. Of course, means must also be provided for unthreading the web of tape (and the leader block) from the apparatus, and for replacing the leader block within its nesting in the 3480 tape cartridge. In connection with such operations, there are two major considerations which have particular pertinence to the present invention.
First, special means must be provided to engage the leader block assembly, and to guide the leader block (and the tape which follows) through the transport apparatus which is to operate upon the web of tape. This requires care in withdrawing the leader block from the tape cartridge, and in guiding the web of tape from the supply reel of the tape cartridge, past the read/write head, and into engagement with the take-up reel which is traditionally provided to cooperate with the supply reel in transporting the web of tape through the apparatus and past the read/write head. This necessitates the development of an appropriate path for threading the leader block through the apparatus, as well as means which have sufficient driving forces to withdraw the leader block from its normally seated position within the tape cartridge, and to replace the leader block within this normally seated position after the tape cartridge has been used. To meet these needs, as well as other design requirements regarding data density and performance characteristics, those devices described in the above-identified United States patents each make use of a loading mechanism which is essentially separate from the remainder of the apparatus which is used to operate upon the magnetic recording tape. In each case, a track or groove is provided for guiding the leader block through the desired tape path and to the take-up reel, under the influence of a dedicated driving means which is separate from the various components comprising the tape transport. Although several different mechanisms are described, in each case a separate motor and track/groove drive is provided to achieve proper interfacing of the web of tape with the apparatus.
Second, as with any magnetic tape recording apparatus, care must be taken to develop a proper tape path between the supply and take-up reels, and across the read/write head, to assure proper registration of the tape with the read/write head. The primary consideration in this regard is one of length, since the tape path must generally be long enough to accommodate distortion of the tape as the web of tape is drawn through the apparatus, as a result of mechanical irregularities in the apparatus. To this end, those devices described in the above-identified patents each provide a tape path of significant length, to account for such potential irregularities. A secondary consideration is that care must be taken to avoid undesirable contact between the oxide coating provided on the web of magnetic recording tape, and components of the apparatus other than the read/write head, such as bearings and idler rollers. When the IBM 3480 tape cartridge is used as intended in the various devices described in the above-identified patents, the oxide coating (formed on the inner most face of the tape on the supply reel) normally faces toward the interior of the transport apparatus due to its orientation. As a result of this placement, as the tape is threaded through the transport apparatus the potential exists for the oxide coating to be drawn across various of the guiding structures associated with the apparatus. Since contact with such structures can compromise the useful life of the tape cartridge, and give rise to a potential for memory loss in the event that portions of the oxide coating become damaged, special care is taken to avoid contact between the oxide coating and those guiding structures which the oxide coating could potentially contact. For example, air-bearings are provided on either side of the read/write head to avoid contact between the bearings and the web of tape which passes across them.
As a result of these and other design considerations, those devices which have been developed to operate upon IBM 3480 tape cartridges have generally been large, cumbersome and expensive. While this can be justified in connection with relatively large, mainframe applications, such design constraints have significantly limited, if not totally precluded use of the 3480 tape cartridge in connection with relatively low cost, minicomputer or microcomputer applications.
Yet another consideration which has inhibited use of the 3480 tape cartridge in mini/micro-computer applications is one of space. It is generally impractical, and therefore undesirable, to necessitate the purchase of an apparatus for off-line, back-up storage or the like which is significantly larger than the primary equipment which the apparatus is to support. In fact, due to the prevalent use of 51/4 inch magnetic recording (floppy) discs in connection with such applications, a de facto standard has come about for any form of storage equipment (floppy disc, hard disc, cartridge, etc.) which is to replace or relate to such conventional storage means. The recognized "form factor" or "footprint" of a standard 51/4 inch magnetic recording disc calls for a container or housing having dimensions on the order of 53/4 inches in width, 8 inches in depth and 31/4 inches in height. Those devices described in the above-identified patents are not adaptable to such applications.
Accordingly, limitations of cost and size have significantly limited the ability to use the IBM 3480 tape cartridge in mini/micro-computer applications. For this reason, efforts have been made to develop other means for adapting 3480 tape cartridges to the 51/4 inch form factor which is desired for such applications. One such system is described with reference to U.S. patent application Ser. Nos. 842,446, now U.S. Pat. No. 4,769,797, and 842,450, entitled "Apparatus for Loading and Unloading the Leader Block of a Tape Cartridge" (Jay Smith); 842,487, entitled "Apparatus for Coupling a Drive Motor to a Leader Block Loading/Unloading Mechanism" (Jay Smith); and 842,448 entitled "Retractable Tape Guide" (Daniel Sachuk), which have been co-filed with the present application, and which are commonly owned by Computer Peripherals, Inc.
Briefly, these patent applications describe a system for engaging the leader block of a 3480 tape cartridge and for guiding the leader block through the transport apparatus using a threading mechanism which is directly associated with the take-up reel of the apparatus, rather than requiring the use of an independent loading mechanism. To accomplish such loading of the leader block in an apparatus where space requirements are to be kept to a minimum, without unacceptably compromising the tape path, and while avoiding contact between the oxide layer on the web of tape and structures other than the read/write head, it has surprisingly been found to be desirable to receive the tape cartridge within the apparatus in an orientation which is rotated 90 degrees from its normally intended orientation. As a consequence of this placement, the oxide coating is oriented so as to avoid contact with guiding structures such as bearings and idler rollers, and the tape path for the web of tape is significantly extended from that which would result from conventional placement of the 3480 tape cartridge within the transport apparatus.
Although such placement of the tape cartridge has enabled the development of an apparatus which can accommodate a 3480 tape cartridge within the 51/4 inch form factor of a conventional disc-type storage apparatus, rotation of the tape cartridge through an angle of 90 degrees has caused certain difficulties. For example, because of this rotation, the slot which is provided in the leader block for engagement by the threading mechanism no longer extends rearwardly from the tape cartridge, but rather extends transversely from a side edge, making engagement of the slot more difficult. Moreover, various ancillary features such as the means which are traditionally provided to prevent data from being recorded over existing data to be retained (so-called write protection) are no longer in their expected location. It therefore became necessary to develop a means for receiving the 3480 tape cartridge, for loading and unloading, in an orientation which is rotated 90 degrees from the normally intended placement of the tape cartridge, without compromising the performance features of the tape cartridge.